What is Komatsu PC120-6 Fault Code E-5?

Fault Code E-5 on the Komatsu PC120-6 excavator indicates a malfunction in the hydraulic pump control system, specifically related to the pump delivery pressure sensor circuit or the pump regulator solenoid. This code triggers when the Electronic Control Unit (ECU) detects abnormal voltage signals, circuit interruptions, or pressure discrepancies that prevent proper hydraulic flow regulation.

This fault is critical for the PC120-6 because it directly impacts the machine's ability to modulate hydraulic pressure based on operational demand. When E-5 activates, the excavator may enter a derate mode or experience reduced hydraulic responsiveness, significantly affecting productivity and potentially causing uneven cylinder operation across the boom, arm, and bucket functions.

Common Symptoms

• Hydraulic system operates sluggishly or fails to respond proportionally to joystick inputs
• Warning lamp illumination on the instrument panel (typically a wrench or diagnostic icon)
• Erratic pump noise or unusual pressure fluctuations during operation
• Loss of simultaneous function capability – inability to perform combined movements smoothly
• Engine may rev higher than normal without corresponding increase in hydraulic power output

Potential Causes

For used PC120-6 excavators, the following issues are frequently responsible for triggering Code E-5:

• Pump pressure sensor failure due to internal diaphragm degradation or contaminated hydraulic fluid
• Damaged wiring harness between the ECU and pump control solenoid – particularly at flex points near the pump mounting area where vibration causes conductor fractures
• Corroded electrical connectors on the pressure sensor or solenoid valve, common in machines exposed to moisture or stored outdoors
• Faulty pump regulator solenoid with stuck spool valve or burnt coil windings
• ECU voltage supply issues stemming from aging ground connections or battery terminal corrosion
• Contaminated hydraulic oil causing sensor port blockage or erratic pressure readings

How to Troubleshoot and Fix Code E-5

Step 1: Visual Inspection Begin by examining the pump pressure sensor and control solenoid wiring harness for visible damage, abrasion, or oil contamination. On used excavators, check connector pins for green corrosion and inspect wire insulation at high-flex zones near the swing bearing and pump bracket. Clean all connectors with electrical contact cleaner.

Step 2: Electrical Testing Using a digital multimeter, measure resistance across the pressure sensor (typically 200-500 ohms depending on specification) with the connector disconnected. Check solenoid coil resistance (usually 8-15 ohms). Verify supply voltage at the sensor connector with ignition on – should read 5V or 12V depending on sensor type. Test ground circuit continuity to the ECU.

Step 3: Pressure Sensor Validation Connect Komatsu diagnostic software (or compatible scan tool) to monitor real-time pressure sensor values. Compare readings against actual system pressure using a mechanical pressure gauge installed at the test port. Discrepancies exceeding 5% indicate sensor failure.

Step 4: Hydraulic System Check Inspect hydraulic filter condition and oil quality. Metallic contamination or degraded fluid can clog sensor ports. For used machines with 5,000+ hours, consider replacing the sensor and cleaning the filter housing before condemning the solenoid.

Step 5: Component Replacement If diagnostics confirm sensor or solenoid failure, use genuine Komatsu parts or OEM-equivalent components rated for the PC120-6's operating pressure range. After replacement, clear codes and perform a complete hydraulic function test.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and seek qualified technician assistance for complex electrical or hydraulic repairs.